Correlation between catch method, condition, and diet patterns in Atlantic cod (Gadus morhua)

Abstract With seal populations increasing significantly in the Baltic Sea, the conflict between seals and fisheries is growing. The most sustainable method for mitigating the seal–fishery conflict is to develop and use seal-safe fishing gear. Although pots have been shown to be a promising alternative to gillnets for catching cod (Gadus morhua), there are indications that cod caught in pots are in poorer condition than those caught in gillnets, potentially making the pots a less-economical alternative. This study investigates whether this difference in condition is consistent over larger spatial scales. Gear-specific cod condition was related to both short-term (determined from stomach contents) and long-term (determined by stable isotope analysis) diet composition. Results indicate that differences in fish condition between gear types are consistent over large areas, possibly due to temporal and spatial differences in feeding strategies. We argue that condition differences between pot- and gillnet-caught cod may be driven by differences in behavioural traits. Consequently, fishing with a certain gear type may have ecological consequences affecting population characteristics, with implications for fisheries management. From the perspective of the seal–fisheries conflict, pots may ultimately have consequences on the catch value of fish.

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Regional variation in otolith geochemistry of juvenile Atlantic cod (Gadus morhua) in coastal Newfoundland

Canadian Journal of Fisheries and Aquatic Sciences ◽

10.1139/cjfas-2015-0353 ◽

2016 ◽

Vol 73 (10) ◽

pp. 1507-1519 ◽

Cited By ~ 5

Author(s):

Ryan R.E. Stanley ◽

Claudio DiBacco ◽

Simon R. Thorrold ◽

Paul V.R. Snelgrove ◽

Corey J. Morris ◽

...

Keyword(s):

Gadus Morhua ◽

Environmental Variability ◽

Atlantic Cod ◽

Environmental Influence ◽

Spatial Scales ◽

Early Life History ◽

Otolith Chemistry ◽

Geographic Patterns ◽

Assignment Success ◽

Scale Classification

We examined spatial variation in otolith geochemistry as a natural tag in juvenile Atlantic cod (Gadus morhua) to resolve geographic patterns during early life history. Individuals from 54 inshore sites spanned five embayments in eastern Newfoundland. Otolith composition differed at all spatial scales and related inversely to spatial scale. Classification analysis revealed increasing discrimination at coarser spatial scales: site (26%–58%), bay (49%), and coast (76%). Assignment success declined by ∼10% per added site with increasing sampling sites per bay, demonstrating fine-scale (<100 km) variation. When we partitioned environmental variability from observed otolith chemistry using predictive models, assignment success improved by 56%, 14%, and 5% for site, bay, and coast, respectively. Our results demonstrate environmental influence on spatial structure of otolith chemistry and illustrate the importance of resolving baseline variability in otolith chemistry when conducting assignment tests. Collectively, our results describe the potential utility of juvenile otolith composition in evaluating contributions of subpopulations to the Northwest Atlantic cod stock and highlight important limitations imposed by environmental variation at scales less than 100 km.

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Small-scale temporal and spatial variation in Atlantic cod (Gadus morhua) life history

Canadian Journal of Fisheries and Aquatic Sciences ◽

10.1139/f03-090 ◽

2003 ◽

Vol 60 (9) ◽

pp. 1111-1121 ◽

Cited By ~ 44

Author(s):

Tara M McIntyre ◽

Jeffrey A Hutchings

Keyword(s):

Body Mass ◽

Life Histories ◽

Gadus Morhua ◽

Atlantic Cod ◽

Spatial Scales ◽

Gonadosomatic Index ◽

Small Scale ◽

Hepatosomatic Index ◽

Georges Bank ◽

High Fecundity

Life histories of Atlantic cod (Gadus morhua) from the Gulf of St. Lawrence south to Georges Bank differ significantly through time and space. Within the Southern Gulf, fecundity per unit body mass differed by more than 40% over short (2 years) and long (4245 years) periods of time. Significant variation in size-specific fecundity is also evident among populations: Southern Gulf cod produce almost 30% more eggs per unit body mass than those on Georges Bank, whereas fecundity of Scotian Shelf cod is almost half that of cod in Sydney Bight. Compared with those on Georges Bank, Southern Gulf cod life histories are characterized by high fecundity, late maturity, high gonadosomatic index, and large eggs. Relative to the influence of body size, neither temporal nor spatial differences in fecundity can be attributed to physiological condition, as reflected by liver weight, hepatosomatic index, and Fulton's K. Delayed maturity and higher reproductive allotment among Southern Gulf cod can be explained as selection responses to slower growth, higher prereproductive mortality, and fewer lifetime reproductive events. Patterns of covariation in heritable, fitness-related traits suggest the existence of adaptive variation and evolutionarily significant units at spatial scales considerably smaller than the species range in the Northwest Atlantic.

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Occurrence and distribution of parasites in relation to food components of grey gurnard, Eutrigla gurnardus (L.) (Teleostei: Scorpaeniformes), off the Shetland Islands

Oceanological and Hydrobiological Studies ◽

10.2478/s13545-014-0140-0 ◽

2014 ◽

Vol 43 (3) ◽

Author(s):

Ewa Sobecka ◽

Beata Więcaszek ◽

Ewa Łuczak ◽

Artur Antoszek

Keyword(s):

Gadus Morhua ◽

Atlantic Cod ◽

Stomach Contents ◽

Food Composition ◽

Parasite Fauna ◽

Intermediate Hosts ◽

Shetland Islands ◽

Grey Gurnard ◽

By Catch ◽

First Time

AbstractThe research was conducted on the parasite fauna and food composition of Eutrigla gurnardus caught as by-catch in commercial catches of the Atlantic cod Gadus morhua near the Shetland Islands. Thirteen species and two genera of pathogens were identified, including six species and one genus recorded for the first time in this host. Copepoda — Euphausiacea dominated in the stomach contents (they are also the intermediate hosts for most of the parasites found), while Gadidae dominated among the fish. A checklist of E. gurnardus parasites is included.

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How to validate a length-based model of single-species fish stock dynamics

Canadian Journal of Fisheries and Aquatic Sciences ◽

10.1139/f06-135 ◽

2006 ◽

Vol 63 (11) ◽

pp. 2531-2542 ◽

Cited By ~ 15

Author(s):

Kasper Kristensen ◽

Peter Lewy ◽

Jan E Beyer

Keyword(s):

Survey Data ◽

Gadus Morhua ◽

Negative Binomial ◽

Atlantic Cod ◽

Population Level ◽

Single Species ◽

Model Complexity ◽

Fish Stock ◽

Statistical Hypotheses ◽

The Baltic

This paper validates a new length-based model of the dynamics of fish stocks or crustaceans by hierarchically testing statistical hypotheses and thereby investigating model complexity. The approach is based entirely on scientific survey data and on determination of the statistical distributions of the number of fish caught per haul in each length class. In our example, the negative binomial distribution is statistically accepted and linked to the population level through the new length-based model. The model is derived from the characteristics of continuous recruitment, individually based growth, and continuous, length-dependent mortality rates. Continuous recruitment with annually varying recruitment peaks and individually based growth was crucial for obtaining a model that could be statistically accepted. Natural mortality was estimated as well by the model. The model was applied to survey data for Atlantic cod (Gadus morhua) in the Baltic. Its simple generic nature, as well as the validation procedure, is useful in studying and understanding life history and stock dynamics.

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Survey gear calibration independent of spatial fish distribution

Canadian Journal of Fisheries and Aquatic Sciences ◽

10.1139/f04-034 ◽

2004 ◽

Vol 61 (4) ◽

pp. 636-647 ◽

Cited By ~ 17

Author(s):

Peter Lewy ◽

J Rasmus Nielsen ◽

Holger Hovgård

Keyword(s):

Gadus Morhua ◽

Atlantic Cod ◽

Survey Design ◽

Fish Distribution ◽

Simulation Studies ◽

Conversion Factors ◽

The Baltic ◽

Standard Software ◽

Track Line ◽

Stock Abundance

Trawl surveys provide important information for evaluation of relative stock abundance fluctuations over time. Therefore, when survey gears or vessels are changed, it is important to compare the efficiency and selectivity of old and new gears and vessels. A method for estimation of conversion factors is developed based on a survey design where paired hauls are taken in the same trawl track line. The method explicitly accounts for changes in fish density caused by trawling disturbance. A generalized linear model for paired hauls catches is analytically derived and the gear conversion and disturbance parameters with their precision are obtained using standard software. Simulation studies carried out additionally showed that the estimated conversion factors were practically unbiased. Because of the independence of the spatial fish distribution, the new method is preferable to the traditional paired hauls design for which it is generally not possible to obtain the statistical properties of the estimated conversion factors. The paper is concluded with suggestions on how to optimize survey design. The method was used to estimate conversion factors for Atlantic cod (Gadus morhua) from Danish gear calibration experiments in the Baltic Sea.

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Depth-dependent vertebral number of Atlantic cod (Gadus morhua) on the Magdalen Shallows and Scotian Shelf: stock mixing or microgeographic trends within populations?

Canadian Journal of Fisheries and Aquatic Sciences ◽

10.1139/f00-218 ◽

2000 ◽

Vol 57 (12) ◽

pp. 2393-2401 ◽

Cited By ~ 5

Author(s):

D P Swain ◽

K T Frank

Keyword(s):

Gadus Morhua ◽

Atlantic Cod ◽

Spatial Scales ◽

Relative Length ◽

Scotian Shelf ◽

Age Classes ◽

Vertebral Number ◽

Size At Age ◽

Stock Mixing ◽

Summer Feeding

We examined spatial variation in the vertebral number of Atlantic cod (Gadus morhua) during the summer feeding season in the southern Gulf of St. Lawrence and on the Scotian Shelf. Mean vertebral number increased significantly with depth in the southern Gulf and on the northeastern Scotian Shelf but not on the southwestern Scotian Shelf. In the southern Gulf, where sampling was most extensive, mean vertebral number increased steadily as depth increased from 25 m to over 175 m. Mean vertebral number was also strongly related to relative length within age-classes, with the larger fish at age having more vertebrae. However, the association between vertebral number and depth could not be attributed to confounding between depth and size at age. These results indicate either unexpected mixing between neighbouring cod populations or unexpected structure at fine spatial scales within cod populations.

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Mitochondrial Cytochrome b DNA Sequence Variation of Atlantic Cod, Gadus Morhua, from the Baltic and the White Seas

Hereditas ◽

10.1111/j.1601-5223.1998.00037.x ◽

2004 ◽

Vol 129 (1) ◽

pp. 37-43 ◽

Cited By ~ 18

Author(s):

Einar Árnason ◽

Pétur Henry Petersen ◽

Snaebjörn Pálsson

Keyword(s):

Dna Sequence ◽

Cytochrome B ◽

Gadus Morhua ◽

Sequence Variation ◽

Atlantic Cod ◽

Mitochondrial Cytochrome ◽

Mitochondrial Cytochrome B ◽

Dna Sequence Variation ◽

The Baltic

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Understanding the release efficiency of Atlantic cod (Gadus morhua) from trawls with a square mesh panel: effects of panel area, panel position, and stimulation of escape response

ICES Journal of Marine Science ◽

10.1093/icesjms/fsu124 ◽

2014 ◽

Vol 72 (2) ◽

pp. 686-696 ◽

Cited By ~ 33

Author(s):

Bent Herrmann ◽

Harald Wienbeck ◽

Junita Diana Karlsen ◽

Daniel Stepputtis ◽

Erdmann Dahm ◽

...

Keyword(s):

Escape Response ◽

Gadus Morhua ◽

Atlantic Cod ◽

Mesh Size ◽

Accumulation Zone ◽

Trawl Fishery ◽

Trawl Fishing ◽

Panel Effects ◽

The Baltic ◽

Stimulation Of

Abstract Based on size selectivity data for more than 25 000 cod (Gadus morhua) collected during experimental trawl fishing with six different codends, all of which included a square mesh panel, we investigated the effect on cod-release efficiency based on the size of the square mesh panel area, position of the square mesh panel, and stimulation of the escape response. Based on the results, we were able to explain why the BACOMA codend, applied in the Baltic Sea cod directed trawl fishery, releases juvenile cod efficiently, whereas other designs, including a square mesh panel with similar mesh size, are less efficient. Our main findings reveal that the release efficiency of the square mesh panel in the BACOMA codend depends largely on the overlap of the square mesh panel and the catch-accumulation zone in the codend, where cod do not have the option of just drifting further back in the trawl when proximate to the panel. On the contrary, the reduction in panel size by 50% did not significantly affect the release efficiency when the panel overlapped with the catch-accumulation zone. It was possible to stimulate an escape response for cod to achieve a release through a square mesh panel positioned away from the catch-accumulation zone. Our findings demonstrated that this release was as efficient as for a panel mounted in the catch-accumulation zone of the codend. Devices that stimulate behaviour may improve the release efficiency of cod through square mesh panels in other fisheries where this is a problem.

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The growing degree-day and fish size-at-age: the overlooked metric

Canadian Journal of Fisheries and Aquatic Sciences ◽

10.1139/f07-003 ◽

2007 ◽

Vol 64 (2) ◽

pp. 375-385 ◽

Cited By ~ 165

Author(s):

Anna B Neuheimer ◽

Christopher T Taggart

Keyword(s):

Growth And Development ◽

Gadus Morhua ◽

Atlantic Cod ◽

Variable Temperature ◽

Spatial Scales ◽

Explanatory Power ◽

Field Studies ◽

Fish Length ◽

Degree Day ◽

Size At Age

Growth rate in ectotherms, including most fish, is a function of temperature. For decades, agriculturalists (270+ years) and entomologists (45+ years) have recognized the thermal integral, known as the growing degree-day (GDD, °C·day), to be a reliable predictor of growth and development. Fish and fisheries researchers have yet to widely acknowledge the power of the GDD in explaining growth and development among fishes. We demonstrate that fish length-at-day (LaD), in most cases prior to maturation, is a strong linear function of the GDD metric that can explain >92% of the variation in LaD among 41 data sets representing nine fish species drawn from marine and freshwater environments, temperate and tropical climes, constant and variable temperature regimes, and laboratory and field studies. The GDD demonstrates explanatory power across large spatial scales, e.g., 93% of the variation in LaD for age-2 to -4 Atlantic cod (Gadus morhua) across their entire range (17 stocks) is explained by one simple GDD function. Moreover, GDD can explain much of the variation in fish egg development time and in aquatic invertebrate (crab) size-at-age. Our analysis extends the well-established and physiologically relevant GDD metric to fish where, relative to conventional time-based methods, it provides greater explanatory power.

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